Tubular flexible bag with lap welded ends

ABSTRACT

A length of plastic material is rolled to form a tube, the ends being lapped and partially welded to leave an access opening to the inside of the bag. The bag is then telescoped over welding die or form having the general configuration of the tube, but axially compressed. The tube is then accordion folded about the thin form so that the ends of the tube can be wrapped around peripheral rims of the form. End pieces are then welded in place, the form is removed through the access opening and the partially welded lap joint forming the access opening is sealed.

nited States 4; atent [1 1 Mollura July 23, 1974 TUBULAR FLEXIBLE BAGWITH LAP 2,398,404 4/1946 Brooks 229/55 WELDED ENDS 2,974,825 3/1961Ross 229/515 Related US. Application Data Division of Ser. No. l70,209,Aug. 9, 197], Pat. No. 3,753,819.

US. Cl. 229/55, 150/.5 Int. Cl 865d 3/10, B65d 5/12, B65d 5/16 Field ofSearch 229/93, 5.5, 4.5; 150/.5,

References Cited UNITED STATES'PATENTS 2/1882 Bone 150/.5

Primary Examiner-William [.Price Assistant Examiner -Stephen P. GarbeAttorney, Agent, or Firm-Flam & Flam [5 7 ABSTRACT A length of plasticmaterial is rolled to form a tube, the ends being lapped and partiallywelded to leave an access opening to the inside of the bag. The bag isthen telescoped over welding die or form having the generalconfiguration of the tube, but axially compressed. The tube is thenaccordion folded about the thin form so that the ends of the tube can bewrapped around peripheral rims of the form. End pieces are then weldedin place, the form is removed through the access opening and thepartially welded lap joint forming the access opening is sealed.

3 Claims, 11 Drawing Figures TUBULAR FLEXIBLE BAG WITH LAP WELDED ENDSThis isa division of application Ser. No. 170,209, filed Aug. 9, 1971,now US. Pat. No. 3,753,819.

BACKGROUND or THE INVENTION a. Field of Invention This invention relatesto fabrication of plastic sheet material and, particularly, to thefabrication of bags usable, for example, as water mattresses.

b. Discussion of Prior Art The easiest method of making a water mattressis to juxtapose two identical layers of plastic material and butt weldthe edges together by solvent, adhesive or heat. When such a bag isfilled with water, the corners move out of square. The resulting baglacks a neat appearance. If the bag is inserted in a rectangular frame,a tight fit at the corners is impossible. Moreover, fluid forces tend toopen the butt weld.

Another known method for making a bag is to form it as a rectangularparallelepiped, with the corners folded substantially the same way as abox is gift wrapped with paper. A neatly formed bag results. But a weldat three and more juxtaposed layers is not reliable.

The ideal arrangement is one in which a rectangular prism has its endsturned inwardly rather than outwardly for placement of rectangular endpieces over them. A lap weld, rather than-a butt weld, is thus providedwith only two layers being welded together. A strong reliable seal isprovided and a square comer results. The problem is how, in anuncomplicated way, such a bag structure can be made. The primary objectof this invention is thus to provide a simple method for making aplastic bag with lap welded ends.

BRIEF SUMMARY OF THE INVENTION In order to accomplish the foregoingobject, a length of plastic material is looped to form a tube. Theoverlapped ends are welded along a line parallel to the tube axis, butan opening is provided in the middle of the weld for access to theinside'of the bag. The bag is then telescoped over a floating die havinga peripheral configuration corresponding to the desired cross-section ofthe tube. However, the axial length of the die does not correspondto thelength of the tube; instead, the die is relatively thin. The sides ofthe tube are accordion folded over the thin die. The die has rims aboutwhich the ends of the tube are inwardly folded and held. End pieces areplaced over the folded tube ends, and the entire assembly is sandwichedbetween electrodes of a dielectric welding machine. Two dielectric gapsare serially connected by the floating die, which is electricallyconductive. The die is removed through the access opening after the lapwelds are formed at the ends. An insulation strip is inserted into thebag to underlie the incompleted axial weld. The axial weld is completed,trapping the. insulation strip inside. Finally, the strip is removedthrough the tiller plug opening.

BRIEF DESCRIPTION OF THE DRAWINGS drawings, unless described asdiagrammatic or unlessotherwise indicated, are to scale.

FIGS. 1 and 2 are diagrammatic views illustrating how a flat sheet ofplastic material (FIG. 1) is looped and partially welded (FIG. 2) toform a tube.

FIGS. 3, 4 and 5 are diagrammatic views illustrating the insertion of awelding die or form into the plastic tube (FIG. 3); the accordionfolding of the tube about the die; the inward folding of the edges ofthe tube ends over the top and bottom rims of the die and the placementof plastic end pieces over the die ends (FIG. 4); and the welding of theend pieces.

FIG. 6 is a fragmentary transverse sectional view illustrating thewelding die and plastic components sandwiched between plates of adielectric welding machine.

DETAILED DESCRIPTION 4 The following detailed description is of the bestpresently contemplated mode of carrying out the invention.

This description is not to be taken in a limiting sense, but is mademerely for. the purpose of illustrating the general principles of theinvention since the scope of the invention is best defined by the'appended claims.

The completed bag shown in FIG. 11 is made from three sheet plasticparts, tube 10, and two'end pieces 12 and 14 closing the ends of thetube. These sheet plastic parts are welded together by heat, generatedin this instance dielectrically by application of a high frequencyelectrical field in the region of the plastic intended to be heated andwelded. Polyvinyl chloride materials are well known plastics used forsuch purposes.

The two end pieces are rectangular whereby the entire bag takes on theconfiguration of a rectangular parallelepiped for use of the bag as awater mattress. All of the welds are lap welds so that the internalfluid pressure is resisted by stressing the weld in shear across itsentire transverse width. Such lap welds areextremely strong as comparedwith butt welds in which internal pressure tends progressively toseparate the abutted welded layers. There are only three lap welds. v

The first lap weld 16 (FIG. 2) joins the ends of a sheet of plasticmaterial (FIG. I). The weld 16 at first is only partly completed,leaving a central gap or opening 18 for purposes to appear hereinafter.

The tube 10 is prepared for lap welding the end pieces 12 and 14 to thefree edges 20 and 22 at the ends of the tube 10. For this purpose, thetube 10 is telescoped over a floating die 24. The die has top and bottomshallow recesses 26 and 28 (see also FIG. 6) that form thin rims 30 and32. The peripheral portions of each rim has the configuration ofintended crosssection of'the completed'mattress and-theprecise con-'figuration of the end pieces 12 and 14.

The distance between the end surfaces 34 and 36 of the die rims issubstantially less than the intended axial length of the tube It). Theend edges 20 and 22 of the tube are, respectively, wrapped inwardlyaround the rims 30 and 32. In order to make this possible, the centralportion of the tube is generally accordion folded or gathered. The sidesof the die between the rims are relieved as at 38 so that the folds areeasily accommodated.

The inwardly wrapped edges and 22 are held on the inside of the rimsabout peripheral walls of the recesses 26 and 28 by the aid of clamps(not shown) or boards (not shown) press fitted into the recesses 26 and28. The end pieces 12 and 14 may now be positioned on the rims inoverlapped relationship to the tube edges 20 and 22 and as indicated inFIG. 4.

The plastic parts so preassembled are sandwiched between two plates Aand B of a dielectric heating machine. The top plate may be the highvoltage electrode and the lower plate may be at ground potential. Aclosing pressure is applied between the plates, bringing the end pieces12 and 14 into firm contact with the end edges 20 and 22 of the tube 10.

The die 24, being made of aluminum or other electrically conductivematerial, forms a capacitor with the upper plate A. The overlappedplastic material at the end surface 34 of the rim 30 forms part of thedielectric of this capacitor. The remaining part of the capacitordielectric is formed by a heat stable dielectric pad 40 of designedthickness. The die 24 similarly forms a capacitor with the lower plateB. The overlapped plastic material at the end surface 36 of the rim 32forms part of the dielectric of this capacitor. The upper and lowercapacitors are electrically in series and the voltage is divided equallybetween them. Upon the application of a suitable high frequency a.c.electrical potential across the plates A and B, heat is generated in thedielectric material and heat welds are formed. The floating die 24 alsoequalizes the mechanical pressure at the top and bottom layers as theplates A and B close.

In practice, the end pieces 12 and 14 are oversize in order to permitpreassembly of plastic parts with the die 24 without unnecessaryattention to alignment. The peripheral portion of the end pieces readilytear away after the weld is formed.

The die 24 is now removed through the gap 18 (FIG. 7). The length of thetube 10 exceeds the width of the tube allowing the die to be turnedpreparatory to removal. Clamps or other devices used to hold theinwardly turned edges pull free from the bag and are removed throughinterior access openings in the die.

The lap weld 16 for the tube part 10 is now completed. In order tocomplete the lap weld, a heat stable flexible dielectric separator 44 isinserted inside the mattress beneath the area where the weld is to becompleted so that the weld does not include the side of the tubeopposite the weld 16. The separator is adhered to one side of a flexiblemetal strip 45 that operates like the die 24 in forming capacitors fordielectric heating.

The mattress with the inserted separator 44 is now dielectrically heatwelded as indicated in FIG. 9.

The separator 44 is now removed through a fill hole 46 (FIG. 10). Thishole was formed in the plastic sheet 10 (FIG. 1) before the sheet wasformed into a tube. The mattress is completed by attaching a valve bodyor connector body 48 at the fill hole 46. If the body 48 has an adequateopening, it can be attached at an earlier stage in the process.

The three lap welds are simple and thus capable of being securely formedby well known dielectric heat welding processes. Since the die 24 floatsbetween two plates A and B, it requires no supporting arm that wouldhave to extend through the access opening 18. Such a supporting armwould unduly complicate the placement of the plastic about the die. Byuse of the floating die, the quick and economical preassembly of all ofthe plastic parts preparatory to simultaneous welding is possible. Thelap welds provide a strong structure, and the corners are perfectlyformed neatly and properly to fit into a rectangular frame.

Intending to claim all novel, useful and unobvious features shown ordescribed, I claim:

1. A lap welded plastic bag in the form of a tube of substantiallyuniform cross-sectional configuration, said bag comprising three plasticsections,

a. one section comprising a sheet of material having ends lapped andwelded together to form said tube;

b. the marginal ends of said tube being inwardly folded to form at eachend of said tube a marginal flange that is unbroken and of singlethickness;

c. the second and third sections being end pieces each having the shapeand dimension of said crosssectional configuration;

d. the marginal edge of each end piece respectively overlying and beinglap welded to the corresponding inwardly folded, single thicknessmarginal flange at the end of said tube;

e. said plastic bag being fluid impervious and flexible;

bly facilitating the filling of said mattress with water.

1. A lap welded plastic bag in the form of a tube of substantiallyuniform cross-sectional configuration, said bag comprising three plasticsections, a. one section comprising a sheet of material having endslapped and welded together to form said tube; b. the marginal ends ofsaid tube being inwardly folded to form at each end of said tube amarginal flange that is unbroken and of single thickness; c. The secondand third sections being end pieces each having the shape and dimensionof said cross-sectional configuration; d. the marginal edge of each endpiece respectively overlying and being lap welded to the correspondinginwardly folded, single thickness marginal flange at the end of saidtube; e. said plastic bag being fluid impervious and flexible; f. theinternal fluid pressure of fluid contained by said bag being resisted bystressing across the entire transverse width of each lap weld joiningsaid sections.
 2. A water mattress consisting of a plastic bag accordingto claim 1, wherein said end pieces are generally rectangular so thatthe bag takes on the configuration of a rectangular parallelopiped whenfilled with water.
 3. A water mattress according to claim 2 furthercomprising a connector assembly attached to said bag and covering a fillhole therein, said connector assembly facilitating the filling of saidmattress with water.